Is π-donation the only way? Unprecedented unsaturated Ru(II) species devoid of π-donor ligands

R. H. Heyn, S. A. Macgregor, T. T. Nadasdi, M. Ogasawara, O. Eisenstein*, K. G. Caulton

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

38 Citations (Scopus)


Reaction of RuHX(CO)L2 (L = PtBu2Me) with tBuLi in pentane or toluene at -40°C gives Ru(H)2(CO)L2 as a reactive and thermolabile square-pyramidal species with inequivalent hydrides (one apical). This molecule forms 1:1 adducts with N2, H2, PH2Ph, PHPh2 or PHCy2, and forms Ru(H)2(CO)2L2, then Ru(CO)3L2 with CO. Oxidative addition of the H-C bond of HC2Ph, the H-Si bonds of SiPh2H2 and SiMe3H and the H-O bond of H2O occurs with elimination of H2, to give RuH(C2Ph)(CO)L2, RuH(SiR3)(CO)L2 and RuH(OH)(CO)L2, respectively. Ru(H)2(CO)L2 reacts with MeI to give RuMeI(CO)L2 and RuHI(CO)L2. Above -40°C, Ru(H)2(CO)L2 hydrogenates isobutylene and subsequently metallates one tBu group of its phosphine, to give RuH(CO)L(P∼C). This strained molecule reacts with arenes to give RuH(aryl)(CO)L2. Reaction of RuHCl(CO)L2 with PhLi provides an alternative synthesis of RuHPh(CO)L2, which rapidly ( ∼2 h) exchanges its H and Ph groups with C6D6 or with toluene. Reaction of RuHPh(CO)L2 with CO gives the much less reactive RuH(Ph)(CO)2L2, while RuHPh(CO)L2 reacts with MeI to give RuMeI(CO)L2 and with EtBr to give first Ru(Et)Br(CO)L2, then RuHBr(CO)L2 and ethylene. N-chlorosuccinimide converts RuHPh(CO)L2 into RuClPh(CO)L2. On a timescale of 2 days, RuH(aryl)(CO)L2, in arene solvent, rearranges to Ru(η6-arene)(CO)L and free L. The structural and electronic properties of the family of unsaturated RuXH(CO)(PH3)2 (X = H, SiH3, CCH, F, Cl, Br, OH, OMe) complexes have been analyzed by core potential ab initio methods at the MP2 level. The preferred structure for each member of this family is calculated to be square-pyramidal with the strongest σ-donor ligand (H or SiH3) at the apical site. Powerful σ-donating groups (i.e., ligands with a strong trans influence: H or SiR3) are found to be very efficient at compensating the electron deficiency at the metal. A π-donating ligand occupies a basal site, trans to the CO group. Due to the lack of a low-lying empty metal dπ orbital (i.e., the molecule is a sigma Lewis acid), π effects are weaker at stabilizing the unsaturation: a push-pull interaction involving the p lone pair(s) of X, the occupied d metal orbital and the π* co orbitals constitutes an additional, but secondary, stabilizing factor. This explains why Ru(H)2(CO)L2 and RuH(SiR3)(CO)L2 are both observable species. The calculated Ru-N bond dissociation energy of RuXH(NH3)(CO)(PH3)2 confirms the dominant role of the σ-donation of the ligands, especially that of the ligand trans to NH3. Thus, compounds of the type RuH(X)(CO)(PR3)2 are better regarded as primarily 'σ-stabilized' 16-electron species whose properties are then finely tuned by π effects.

Original languageEnglish
Pages (from-to)5-26
Number of pages22
JournalInorganica Chimica Acta
Issue number1-2
Publication statusPublished - Jun 1997


  • Ruthenium complexes
  • Unsaturated complexes


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